I was going to suggest the same thing as @shatteredsquare but I use plain old Turtle Wax paste. It's an old car show trick that makes the glass look invisible.
Regardless of what you apply to the glass, it is critically important that you get
everything off the glass first. I use rubbing alcohol and paper towels. I know I've got all the stuff off when it suddenly becomes harder to move the paper towel across the glass.